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Fig. 4. Cross-sections showing variations in ground water tritium activity (TU) along three transects (W2, W1, and W1rip) during June 2001. Tritium contours are interpreted as pre-1953 in age for waters with tritium activity of <3 TU, whereas values of >12 TU show an influence of "bomb-peak" precipitation between 1963 and 1980. Intermediate values indicate recent or mixed-age waters. Piezometers not sampled for tritium are indicated by a crossed symbol. Piezometer-nest identifiers are shown along the land surface. Refer to Fig. 1 and Table 2 for piezometer-nest and cross-section locations and identifiers.
